Over the last 20 years, the interest in the human gut microbiome has increased tremendously due to its close association with gut health. They are a community of over 200 different bacteria, virus, and fungi that have inhabited the gastrointestinal tract, and each have their unique features and functions for the human body. Findings have shown that an imbalance in these microbiomes leads to the pathogenesis of various diseases – whether they are gut-related or not. These may include Type 2 Diabetes, Inflammatory Bowel Disease, Cardiovascular Diseases, and even Colorectal Cancers. (1)

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What is the Gut Microbiome?

The Gut Microbiome includes all the different genomes of microorganisms that live in the gut. These have been studied in the past using different methods – the most common of which is to isolate and culture each specie. Another method that may be used is known as Metagenomics which is associated with the reconstruction of microorganisms from a stool sample. (2)

The Functions of Gut Microbiome

The Microbiomes in the gut has several important functions. These include protection from infection-causing substances and pathogens and ensuring continuous differentiation and regeneration of the colonocytes already present in the gut. It does this by producing sufficient energy for the colonocytes by ensuring the fermentation of carbohydrates from the diet to produce short-chain fatty acids. (3)

The microbiota also has the ability to produce different vitamins and amino acids in the gut, along with promoting regular fat metabolism. (4) Studies have also shown the Microbiome to be able to interact with the immune cells and improve the immune system of the body. An example of this is the anti-inflammatory ability of the Microbiome, as it is able to inhibit the deacetylation of histones and regulate T cell's function. (5)

Dana-Farber Cancer Institute 

Diet Patterns and Gut Microbiota

Numerous studies have proven diet to be a primary factor maintaining and promoting the diversity of  Gut Microbiota – in turn ensuring the resilience of the human gut. Changes in diet can lead to changes in the type and functionality of the gut microbiota rapidly. This has sparked an interest in the association between diet, microorganisms in the gut, and host health over the past few years, leading to an increasing number of clinical trials being conducted. Moreover, different diets like Western Diets, Mediterranean diets, and vegan diets have been studied carefully and how each of these is able to affect the diversity and composition of the microorganism found in the gut. (6)

The Western Diet, which is primarily based on saturated fats, salt, sugar, and low fibers, is opted by the majority of the population in the fast-paced world that we live in today. These carbohydrates present in such a  diet are also known as Microbiota accessible carbohydrates, which are able to alter the Gut Microbiota not only structurally but functionally as well. (7) It can lead to increased production of mucus degrading agents in the gut and promote the enrichment of anti-biotic resistant and bile tolerant microorganisms. (8)

Ways to Optimize Gut Health

There are several ways to improve gut health. However, the ones which are proven to be effective by science include regular exercise, a high fiber diet, and smoking cessation. 

Exercise

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Regular exercise is promoted by health experts all over the world for its ability to not only regulate one's weight and metabolic activity but also prevent the incidence of conditions like diabetes by improving insulin sensitivity. However, recent studies have shown that exercise may also be able to alter the intestinal microbiota and improve gut health.

One such study conducted on animal subjects who were made to undergo five weeks of regular exercise training showed an increased production of short fatty acids chains – which is a fermentation product of dietary fibers by bacteria in the gut. This also leads to an increase in the number of the therapeutic bacteria responsible for this known as. The increase in this bacteria is associated with the proliferation of epithelial cells in the gut, regulation of the immune system and gene expression, and the promotion of the integrity of the gut barrier. (9)

High Fiber Diets

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A high fiber diet which is accompanied by high water intake is often recommended for the maintenance of gut health. Moreover, foods that are high in proteins and low in saturated and Trans fat are also recommended for the prevention of gut disorders and dysbiosis. These diets may include vegan diets, which are usually high in fibers, and high proportions of plant-based foods which are fermented by the gut microorganism. Studies conducted on this diet showed it to reduce the production of harmful and disease-causing bacteria like Bacteroides – as compared to uncontrolled diets. (10)

Smoking Cessation

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Smoking Cessation (quitting) is found to be associated with an increase in beneficial bacteria for the gut and the reduction of pathogenic organisms like Bacteroidetes and Proteobacteria. It also leads to an increase in microbial diversity to allow the gut to stay protected from infections and diseases. Studies conducted on this showed a difference in the composition of intestinal microbiota in smokers and nonsmokers. (11) 

Moreover, these changes in the microbiota are not only limited to the intestinal but also include components of the upper respiratory tract, throat, saliva in the mouth, and sputum in the throat. Moreover, taking regular nicotine can also increase gut permeability, which leads to poor health of patients with inflammatory bowel disease. This increased gut permeability is due to the disintegration of the tight intercellular junctions, which negatively affects the barrier function of the gut and leads to an increased incidence of pathologies. (12) 

The health of the gut and the individuals generally is highly dependent on the composition and diversity of the Microbiome of the gut. Hence in order to stay healthy, it is essential to focus on the factors which improve the gut microbiota, which includes maintaining regular exercise, preventing nicotine intake, and consuming diets rich in fibers and low in saturated fats. 

References:

1. Conlon, M. A., & Bird, A. R. (2014). The impact of diet and lifestyle on gut microbiota and human health. Nutrients, 7(1), 17–44. https://doi.org/10.3390/nu7010017

2. Hills RD Jr, Pontefract BA, Mishcon HR, Black CA, Sutton SC, Theberge CR. Gut Microbiome: Profound Implications for Diet and Disease. Nutrients. 2019;11(7):1613. Published 2019 Jul 16. doi:10.3390/nu11071613

3. Berer, K., & Krishnamoorthy, G. (2014). Microbial view of central nervous system autoimmunity. FEBS letters, 588(22), 4207–4213. https://doi.org/10.1016/j.febslet.2014.04.007

4. Frick, J. S., & Autenrieth, I. B. (2013). The gut microflora and its variety of roles in health and disease. Current topics in microbiology and immunology, 358, 273–289. https://doi.org/10.1007/82_2012_217

5. Gensollen, T., Iyer, S. S., Kasper, D. L., & Blumberg, R. S. (2016). How colonization by microbiota in early life shapes the immune system. Science (New York, N.Y.), 352(6285), 539–544. https://doi.org/10.1126/science.aad9378

6. Yadav, M., Verma, M. K., & Chauhan, N. S. (2018). A review of metabolic potential of human gut microbiome in human nutrition. Archives of microbiology, 200(2), 203–217. https://doi.org/10.1007/s00203-017-1459-x

7. Sonnenburg, E. D., & Sonnenburg, J. L. (2014). Starving our microbial self: the deleterious consequences of a diet deficient in microbiota-accessible carbohydrates. Cell metabolism, 20(5), 779–786. https://doi.org/10.1016/j.cmet.2014.07.003

8. Sonnenburg, J. L., & Sonnenburg, E. D. (2019). Vulnerability of the industrialized microbiota. Science (New York, N.Y.), 366(6464), eaaw9255. https://doi.org/10.1126/science.aaw9255

9. Evans, C. C., LePard, K. J., Kwak, J. W., Stancukas, M. C., Laskowski, S., Dougherty, J., Moulton, L., Glawe, A., Wang, Y., Leone, V., Antonopoulos, D. A., Smith, D., Chang, E. B., & Ciancio, M. J. (2014). Exercise prevents weight gain and alters the gut microbiota in a mouse model of high fat diet-induced obesity. PloS one, 9(3), e92193. https://doi.org/10.1371/journal.pone.0092193

10. Wu, G. D., Compher, C., Chen, E. Z., Smith, S. A., Shah, R. D., Bittinger, K., Chehoud, C., Albenberg, L. G., Nessel, L., Gilroy, E., Star, J., Weljie, A. M., Flint, H. J., Metz, D. C., Bennett, M. J., Li, H., Bushman, F. D., & Lewis, J. D. (2016). Comparative metabolomics in vegans and omnivores reveal constraints on diet-dependent gut microbiota metabolite production. Gut, 65(1), 63–72. https://doi.org/10.1136/gutjnl-2014-308209

11. Kobayashi, T., & Fujiwara, K. (2013). Identification of Heavy Smokers through Their Intestinal Microbiota by Data Mining Analysis. Bioscience of microbiota, food and health, 32(2), 77–80. https://doi.org/10.12938/bmfh.32.77

12. 12. Miele, L., Valenza, V., La Torre, G., Montalto, M., Cammarota, G., Ricci, R., Mascianà, R., Forgione, A., Gabrieli, M. L., Perotti, G., Vecchio, F. M., Rapaccini, G., Gasbarrini, G., Day, C. P., & Grieco, A. (2009). Increased intestinal permeability and tight junction alterations in nonalcoholic fatty liver disease. Hepatology (Baltimore, Md.), 49(6), 1877–1887. https://doi.org/10.1002/hep.22848